plugeth/p2p/enode/iter.go

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// Copyright 2019 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package enode
import (
"sync"
"time"
)
// Iterator represents a sequence of nodes. The Next method moves to the next node in the
// sequence. It returns false when the sequence has ended or the iterator is closed. Close
// may be called concurrently with Next and Node, and interrupts Next if it is blocked.
type Iterator interface {
Next() bool // moves to next node
Node() *Node // returns current node
Close() // ends the iterator
}
// ReadNodes reads at most n nodes from the given iterator. The return value contains no
// duplicates and no nil values. To prevent looping indefinitely for small repeating node
// sequences, this function calls Next at most n times.
func ReadNodes(it Iterator, n int) []*Node {
seen := make(map[ID]*Node, n)
for i := 0; i < n && it.Next(); i++ {
// Remove duplicates, keeping the node with higher seq.
node := it.Node()
prevNode, ok := seen[node.ID()]
if ok && prevNode.Seq() > node.Seq() {
continue
}
seen[node.ID()] = node
}
result := make([]*Node, 0, len(seen))
for _, node := range seen {
result = append(result, node)
}
return result
}
// IterNodes makes an iterator which runs through the given nodes once.
func IterNodes(nodes []*Node) Iterator {
return &sliceIter{nodes: nodes, index: -1}
}
// CycleNodes makes an iterator which cycles through the given nodes indefinitely.
func CycleNodes(nodes []*Node) Iterator {
return &sliceIter{nodes: nodes, index: -1, cycle: true}
}
type sliceIter struct {
mu sync.Mutex
nodes []*Node
index int
cycle bool
}
func (it *sliceIter) Next() bool {
it.mu.Lock()
defer it.mu.Unlock()
if len(it.nodes) == 0 {
return false
}
it.index++
if it.index == len(it.nodes) {
if it.cycle {
it.index = 0
} else {
it.nodes = nil
return false
}
}
return true
}
func (it *sliceIter) Node() *Node {
it.mu.Lock()
defer it.mu.Unlock()
if len(it.nodes) == 0 {
return nil
}
return it.nodes[it.index]
}
func (it *sliceIter) Close() {
it.mu.Lock()
defer it.mu.Unlock()
it.nodes = nil
}
// Filter wraps an iterator such that Next only returns nodes for which
// the 'check' function returns true.
func Filter(it Iterator, check func(*Node) bool) Iterator {
return &filterIter{it, check}
}
type filterIter struct {
Iterator
check func(*Node) bool
}
func (f *filterIter) Next() bool {
for f.Iterator.Next() {
if f.check(f.Node()) {
return true
}
}
return false
}
// FairMix aggregates multiple node iterators. The mixer itself is an iterator which ends
// only when Close is called. Source iterators added via AddSource are removed from the
// mix when they end.
//
// The distribution of nodes returned by Next is approximately fair, i.e. FairMix
// attempts to draw from all sources equally often. However, if a certain source is slow
// and doesn't return a node within the configured timeout, a node from any other source
// will be returned.
//
// It's safe to call AddSource and Close concurrently with Next.
type FairMix struct {
wg sync.WaitGroup
fromAny chan *Node
timeout time.Duration
cur *Node
mu sync.Mutex
closed chan struct{}
sources []*mixSource
last int
}
type mixSource struct {
it Iterator
next chan *Node
timeout time.Duration
}
// NewFairMix creates a mixer.
//
// The timeout specifies how long the mixer will wait for the next fairly-chosen source
// before giving up and taking a node from any other source. A good way to set the timeout
// is deciding how long you'd want to wait for a node on average. Passing a negative
// timeout makes the mixer completely fair.
func NewFairMix(timeout time.Duration) *FairMix {
m := &FairMix{
fromAny: make(chan *Node),
closed: make(chan struct{}),
timeout: timeout,
}
return m
}
// AddSource adds a source of nodes.
func (m *FairMix) AddSource(it Iterator) {
m.mu.Lock()
defer m.mu.Unlock()
if m.closed == nil {
return
}
m.wg.Add(1)
source := &mixSource{it, make(chan *Node), m.timeout}
m.sources = append(m.sources, source)
go m.runSource(m.closed, source)
}
// Close shuts down the mixer and all current sources.
// Calling this is required to release resources associated with the mixer.
func (m *FairMix) Close() {
m.mu.Lock()
defer m.mu.Unlock()
if m.closed == nil {
return
}
for _, s := range m.sources {
s.it.Close()
}
close(m.closed)
m.wg.Wait()
close(m.fromAny)
m.sources = nil
m.closed = nil
}
// Next returns a node from a random source.
func (m *FairMix) Next() bool {
m.cur = nil
for {
source := m.pickSource()
if source == nil {
return m.nextFromAny()
}
var timeout <-chan time.Time
if source.timeout >= 0 {
timer := time.NewTimer(source.timeout)
timeout = timer.C
defer timer.Stop()
}
select {
case n, ok := <-source.next:
if ok {
// Here, the timeout is reset to the configured value
// because the source delivered a node.
source.timeout = m.timeout
m.cur = n
return true
}
// This source has ended.
m.deleteSource(source)
case <-timeout:
// The selected source did not deliver a node within the timeout, so the
// timeout duration is halved for next time. This is supposed to improve
// latency with stuck sources.
source.timeout /= 2
return m.nextFromAny()
}
}
}
// Node returns the current node.
func (m *FairMix) Node() *Node {
return m.cur
}
// nextFromAny is used when there are no sources or when the 'fair' choice
// doesn't turn up a node quickly enough.
func (m *FairMix) nextFromAny() bool {
n, ok := <-m.fromAny
if ok {
m.cur = n
}
return ok
}
// pickSource chooses the next source to read from, cycling through them in order.
func (m *FairMix) pickSource() *mixSource {
m.mu.Lock()
defer m.mu.Unlock()
if len(m.sources) == 0 {
return nil
}
m.last = (m.last + 1) % len(m.sources)
return m.sources[m.last]
}
// deleteSource deletes a source.
func (m *FairMix) deleteSource(s *mixSource) {
m.mu.Lock()
defer m.mu.Unlock()
for i := range m.sources {
if m.sources[i] == s {
copy(m.sources[i:], m.sources[i+1:])
m.sources[len(m.sources)-1] = nil
m.sources = m.sources[:len(m.sources)-1]
break
}
}
}
// runSource reads a single source in a loop.
func (m *FairMix) runSource(closed chan struct{}, s *mixSource) {
defer m.wg.Done()
defer close(s.next)
for s.it.Next() {
n := s.it.Node()
select {
case s.next <- n:
case m.fromAny <- n:
case <-closed:
return
}
}
}